Make sure you scrape the chrome plating off the rim part. Also on older tires that have the molded web in the center make sure you trim that good so both the rim and backers fit nicely without having to hold them or wrestle with them. Look to see what surfaces between the rim and backers are touching...then insert rim....put a thin layer of superglue around the mating surface insert the backer and squeeze together for 20 seconds.

your welcome. Also on those molded web tires...i find squeezing the tire so the side wall folds outward helps in trimming the left over nubs..also make sure we're you trim your rims/backers off the parts tree you take time to really carefully trim the nubs that are left...they can make the tire pull away from the rim bead making assembly harder and the look hokey

And as I've been learning more and more test fit, test fit, test fit can't do too much of that. Especially on rims you seem to see imperfections in were you trimmed them off the tree more when they are in the black tire...so don't be afraid to trim ever so slightly and fit a number of times till they look perfect.

Break out the scale sized tire mounting gear. Don't laugh, I trim the tires well and then do something else. I put together the wheels and backs Before I worry about the tires. Those tires are sitting there waiting for their Medium to Hot water bath. Yes, a Hot water bath!

Why? well this makes them supple. Very supple. I just slide them over the rims from the back and then they fit super and they never come apart. Why? because I glued all that stuff together and give it at least a day to dry BEFORE mounting the tires. This has worked for me since they got away from solid tires.